Line-narrowed gas laser system

Abstract

In a line-narrowed gas laser system such as a line-narrowed molecular fluorine laser system, ASE is cut off to obtain a spectral linewidth of 0.2 pm or lower and a spectral purity of 0.5 pm or lower. The laser system comprises a laser chamber filled with an F2-containing laser gas, discharge electrodes located in the laser chamber, a laser resonator and a line-narrowing module located in the laser resonator with a wavelength selection element, so that a line-narrowed laser beam emerges from the laser resonator. To cut off ASE from the laser beam emerging from the laser resonator, the duration from laser emission by discharge to generation of a laser beam is preset. Rise of the sidelight is made so gentle that the starting point of a laser pulse can exist after the time of the first sidelight peak.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates generally to a line-narrowed gas laser system, and more particularly to a gas laser system such as an F2 laser system in which laser beams are narrowed to a spectral linewidth of 0.2 pm or lower and a spectral purity of 0.5 pm or lower while ASE (amplified spontaneous emission) is substantially cut off from the laser beams.[0002]The present invention is also concerned with a gas laser system using laser gases inclusive of F2, for instance, a KrF or ArF laser system, in which the ASE is cut off from laser beams, thereby making spectral linewidths and spectral purities by far narrower.[0003]As semiconductor integrated circuits become increasingly fine with increasing packing densities, aligners used for their fabrication are now required to have stronger resolving power than ever before. It is in turn required to make shorter the wavelengths of exposure light emitted from exposure light sources. To this end, semiconductor ...

AI Technical Summary

Benefits of technology

The present invention provides a gas laser system using an F2-containing laser gas, such as a KrF or ArF laser, with improved line-narrowing capabilities. The system includes a laser chamber, discharge electrodes, a laser resonator, and a line-narrowing module with a wavelength selection element. The system is designed to cut off ASE from the laser beam and achieve a spectral linewidth of 0.2 pm or lower and a spectral purity of 0.5 pm or lower. The system can also include a discharge emission detector and a laser pulse detector for better control of the laser gas pressure and voltage. Overall, the invention provides a more efficient and effective gas laser system for various applications.

Problems solved by technology

One grave problem with photolithography is how to correct chromatic aberrations in an optical system.

By virtue of some limitations on the types of available optical materials transparent to a wavelength range in the neighborhood of 157 nm, however, there is now no option but to use CaF2 (fluorite).

However, the catadioptric systems are not so often used as conventional dioptric systems by virtue of difficulties with the optical axis alignment of aligners.

Even when such an optical line-narrowing module having a spectral function in the laser resonator is used as the line-narrowing means for a line-narrowed F2 laser system, it is still difficult to narrow its spectral linewidth (FWHM) to 0.2 pm or less demanded for the dioptric system of an aligner.

When it comes to an aligner light source, however, there are some limitations on system size at a worksite and, hence, some limitations on the size of a line-narrowing module used thereat.

Thus, there are limits to increasing the number of expanding prisms and the width of the diffraction grating.

There are also limits ascribable to optical part fabrication techniques.

For instance, the blaze angle cannot possibly be larger than a predetermined value because of limits to diffraction grating fabrication.

Even with pulse stretching, however, it is still difficult to narrow the spectral linewidth (FWHM) to 0.2 pm or less.

With the laser pulse waveform containing the ASE, on the other hand, it is difficult to satisfy the specifications of an aligner light source in terms of spectral purity.

It is thus impossible to satisfy the specifications regarding the spectral purity although depending on what is demanded for an aligner.

While the values of the spectral linewidth and spectral purity demanded vary with wavelenth, it is understood that such problems as mentioned above arise with KrF and ArF laser systems.

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